While I don't like the whole "psionics is different than magic" thing, I can't keep track of who wants it separate and who doesn't. So, if you don't want magic for psionics and want to use "psionics is different" then the Avatar is a non-magic class that does the stuff that a Warlord does.
Psionics are still overtly supernatural, though, even if they aren't technically magic (and, by default, it appears that as of this latest iteration, they are technically magic). Ironically, though, in as much as I'm in a psionics camp, at all, I'm more in the 'psionics are different' camp than I used to be (when I just didn't want psionics in the game, at all, but was willing to 'compromise' by functionally erasing the difference between psionics and magic, which, in retrospect, wasn't terribly fair). As it stands, I'm still not a big fan of psionics, but I feel strongly that the magic/not-magic option should be there so that DMs can conveniently decide the role psionics has in their world.
The Cleric's schtick is "character that channels divine power". Divine power is "power that comes from a deity or similar entity". By definition, a Cleric must be affiliated with a deity or some such.
Unless forces and philosophies can be considered 'similar entities.' For instance, the 2e 'Divinity of Mankind' philosophy posited that humanity was, collectively, divine in nature. It also worked well in 2e, in that lower-level spells were explicitly a result of faith and devotion, not directly powered by the deity nor delivered by an intermediary. So a philosophy that wasn't really in touch with any divine entity however much you stretch the term was running on pure faith (delusion) and could only ever get 4th level spells.
Of course, you can reskin it and do whatever you want.
Re-skinning is easy enough, but 5e doesn't push acceptance of that approach the way it does DM Empowerment. More the opposite: the 5e class design philosophy is to evoke class concepts with distinct mechanics & progressions, even if they may seem to be arbitrarily distinct for the sake of being distinct. That creates an expectation of fluff-crunch coupling, or fluff determining crunch (or vice versa) that's antagonistic to re-skinning.
Maybe it's because it's been a while since I had the book, but the Avatar doesn't seem quite as Cleric-y as I remember the Ardent being. Nothing that couldn't get solved by a longer list of Disciplines, though.
The Cleric isn't quite as cleric-y in some minor ways, I suppose. 5e, with it's slower pace of releases, and it's attempt to get so many classes into the PH while still feeling 'light' just doesn't have quite the depth of material other editions did (it exceeds 0e & 1e, I'd think).
I guess I just don't really care much about the difference.
Sounds like you're not qualified to judge the significance of that difference, then, especially to those who do care.
The Ardent has been it's own class in not one but two past editions. It's bad enough getting demoted to a sub-class, and having your name changed to something that makes no sense ('the Avatar?' Of which deity?), without /also/ being mistaken for some other class!
On a different note - I really don't want to see the Soulknife as a Rogue subclass, simply because why not a Ranger or Fighter subclass? The original Soulknife wasn't particularly a sneaky skill-monkey with occasional stabbings, which is what the 5E Rogue really is.
A 5e rogue can make with the SA prettymuch every round. I'd agree in as much as Fighter seems equally legit, but then fighter could get a psychic warrior sub-class.
